Pushbutton cantilevered leaf spring contact switch assembly for keyboard type switch arrays

ABSTRACT

A low profile electromechanical keyboard switch, displaying very low electrical bounce. The switch key top bears against a generally cylindrical plunger which has a depressed flat portion on its side engageable with a tactile ball biased by a spring nested in the switch housing. Upon application of a force to the key top which exceeds a threshold value, the tactile ball is displaced from the flat and over the shoulder defined between the depressed flat and the cylindrical portion of the plunger. Sudden, positive movement of the plunger against an underlying contact leaf ensues. The contact leaf is branched into multiple contact fingers, and arranged with respect to an underlying contact plate so that wiping contact occurs between fingers and plate. The switch housing is configured to carry sufficient diodes and resistors to assure full control and encoding functions in the keyboard in which such switch may be mounted.

United States Patent 1 Brady [451 July 17, 1973 [75] Inventor: John F. Brady, Clifton, NJ.

[73] Assignee: Universal Technology, Inc., Verona,

221 Filed: May 18, 1971 211 Appl. No.: 144,605

[52] US. Cl. 200/159 A, 200/5 A [51] Int. Cl. I10lh 13/66 [58] Field of Search 200/5 R, 5 A, 6 R,

200/6 BA, 6 BB, 6 C, 159 R, 159 A, 166 SD,

166 BH, 166 J [56] References Cited UNITED STATES PATENTS 3,290,439 12/1966 Willcox et a1. 200/5 A X 3,240,885 3/1966 Grunfelder et a1. 200/5 A 2,964,986 12/1960 Johnson 200/5 A X 1,226,971 5/1917 Hart 200/166 SD UX 3,584,162 6/1971 Krakinowski 200/5 A 3,627,935 12/1971 Spievak 3,178,522 4/1965 .Passarelli, Jr. 200/6 C 2,991,343 7/1961 Norden 200/159 R X Primary Examiner.1. R. Scott Attorney-D. S. Edmonds, David .1. Toomey et al.

. [57] ABSTRACT A low profile electromechanical keyboard switch, displaying very low electrical bounce. The switch key top bears against a generally cylindrical plunger which has a depressed flat portion on its side engageable with a tactile ball biased by a spring nested in the switch housing. Upon application of a force to the key top which exceeds a threshold value, the tactile ball is displaced from the flat and over the shoulder defined between the depressed flat and the cylindrical portion of the plunger. Sudden, positive movement of the plunger against an underlying contact leaf ensues. The contact leaf is branched into multiple contact fingers, and arranged with respect to an underlying contact plate so that wiping contact occurs between fingers and plate.

The switch housing is configured to carry sufficient diodes and resistors to assure full control and encoding functions in the keyboard in which such switch may be mounted.

14 Claims, 9 Drawing Figures Ptgnted July 17, 1973 Y v 4 Sheets-Sheet 1 INVENTOR JOHN F. BRADY ATTORNEY I Patenfcd' July 17,1973

'4 Sheets-Sheet 2 INVENTOR JOHN F BRADY ATTORNEY 4 Sheets-Sheet 5 iv w I m GI 5. mm. m orm .m mm mm AT TOR NE Y Patented Jul 17, 1 973* I 3,746,816

" 4 Sheets-Sheet 4 FIG. 5

NTOR

JOH BRADY Stag WW ATTORNEY 1 PUSHBUTTON CANTILEVERED LEAF SPRING CONTACT SWITCH ASSEMBLY FOR KEYBOARD TYPE SWITCH ARRAYS BACKGROUND OF INVENTION This invention relates generally to electrical switches, and more specifically relates to switches adapted for use in the keyboards commonly employed atcomputer terminals or similar environments where'at operator communication with an electronic system occurs.

Electric keyboards featuring an array of individual key switches have been in use for many years. Such keyboards have, for example, long been utilized in electric typewriters, in whichenvironment activation of the individual keys effects striking of the'type face-bearing elements against the typewriter platen. In still more recent years, in consequence of the enormous proliferation in data processing and'communications systems, increased interest in keyboards and particularly in the switches utilized therewith hasbeen evident. This has occurred by .virtue of'the fact that communication with the cited systems is commonly effected through a manually operated keyboard. In particular an operator desiring to enter information into the system or query the system withrespectto information already stored therein, will manually depress appropriate keys at the keyboard to enter data or initiate development of-desired information. i

. Although there arepresently a very large. variety of switches being usedin keyboard environments, it can generally be saidthat the bulk of such switches are either in the nature of solid state devices based for example on the well-known Hall effect or elseare electromechanical in nature.

In the case of the aforementioned solid state switches it is possible to achieve high reliability, long service life, and'flexibility of encodingpbut these switches are technologically quite complex, and in consequence are very expensive in comparison to a functionally similar electromechanical device. By their very nature in essence they are contactless such switches are also lacking in-a feature that isoften much desired in a keyboard environment. In particular it is often of both psychological and practical significance that'a tactile response be fed back to the operator of the keyboard indicating to him that positive activationof the touched keyhas occurred. Such tactile feedback is sufficiently important occurringfor example by a sensed displacementof-the key thatin some instances electrically nonfunctional artifice has been resorted to to produce the desired tactile indication that positive activation of the key has been effected.

Electromechanical switches, with some exceptions,.

usually employ a movable contact of such'nature as can provide a degree of tactile feedback t the operator, indicative of-closing of the switch elements. As was mentioned in connection with the solid state devices, however, many of the electromechanicaldevices such as for example the well-known dryreed switch are also sufficiently expensive as to create competitive disadvantages for the manufacturer who employs large numbers thereof in his equipment; Reed switchesin particular are also characterized by such extended length that it has proved difficult to design akeyboard employing them which is possessed ofa markedly low profile.

Among. the many other attempts to produce a low cost effective switch element, note may be taken, for example, of those recently introduced keyboard switches incorporating a plastic membrane which is deformable by key top movement to effect desired electrical contact. While the cited designs are indeed very compact, and from a cost viewpoint relatively cheap to manufacture, the reliability of these devices appears relatively low.

It may further be noted in connection with the discussion of electromechanically based keyboard switches, that a central problem presented by the bulk of these devices, is that of so-called bounce. In particular it is found upon closing of representative of these switches such as a reed switch that the elements brought into contact to close the electrical circuit tend to oscillate or bounce with respect to one another for a transient period. During this transient bounce period, corresponding oscillations in the potential levels are present at the circuit controlled by the switch. With typical electromechanical switches the cited period of bounce is so prolonged that it is often necessary to incorporate electrical delay means to assure that the output from the switched circuit is not utilized prior to expiration of the bounce period.

In accordance with the foregoing, it may be regarded as an objectof the present invention, to provide a keyboard switch that is of compact, low profile design, that is economical to produce, and that possesses long and dependable operating life.

It is a further object of the invention, to provide an electromechanical keyboard switch which by virtue of the construction clearly and positively closes upon operator depression, which yields excellent tactile feedback to the operator thereof, and which, further, displays minimal mechanical and electrical bounce effects.

It is a still further object of the present invention, to provide an electromechanical keyboard switch configured to compactly carry in self-contained fashion, sufficient diodes and resistors to enable full control and encoding functions in the keyboard at which such switch may be readily mounted.

SUMMARY OF THE INVENTION 'Now in accordance with the present invention, the foregoing objects, and others as will become apparent in the course of theensuing specification, are achieved in an electromechanical keyboard 7 switch so con structed that the switch keytop bears against a generally cylindrical plunger having a depressed flat portion on one side thereof. A spring nested in the switch housing, biases a tactile ball against the flat when the key is in an'undepressed condition. The shoulder defined between the flat and the remainder of the plunger body then provides a stop adjacentthe ball whereby resistance to longitudinal movement of the plunger is provided; When the operator applies a force to the key top which exceeds a threshold value, the tactile ball is displaced from the flat and over the said shoulder defined between the flat and the cylindrical portion of the plunger. Sudden, positive movement of the plunger against an underlying contact leaf ensues. The contact leaf is branchedinto multiple contact fingers, and arranged with respect to an underlying contactplate so that wiping contact occurs between fingers and plate. The switch housing is configured to carry in completely BRIEF DESCRIPTION OF DRAWINGS The invention is diagrammatically illustrated, by way of example, in the drawings appended hereto, in which:

FIG. 1 is an isometric, exploded view of a keyboard switch in accordance with the invention;

FIG. 2 is an isometric, cutaway view of the switch of FIG. 1, showing elements of the switch in their assembled relationship;

FIGS. 3, 3A and 3B are respectively a side view of the switch plunger, an end view thereof, and a side view taken from the side bearing the flat for receiving the tactile ball thereagainst;

FIG. 4 is a plan view of the key top, looking inwardly from the open end thereof;

FIG. 4A is a sectional view of the key top of FIG. 4, taken along the line A-A thereof;

FIG. 5 is a plan view of the housing portion of the FIG. 1 switch; and

FIG. 5A is a sectional view of the housing of FIG. 5, taken along the line A-A therein.

- DESCRIPTION OF PREFERRED EMBODIMENT In FIG. 1 an isometric, exploded view appears, of a keyboard switch 1 in accordance with the present invention. The switch 1 is seen to include generally a housing 3, key top 11, and plunger 9, all molded or otherwise formed ofa nonconduc tive plastic such as nylon or the like, and a pair of electrically conductive elements in the form ofa contact plate 5 and a contact leaf 7.

I The housing 3, which can be seen both in FIG. 1 and in the detail showings of FIGS. 5 and 5A, is a generally box-shaped member, the interior of which is formed with a plate support platform 41 which is stepped outwardly at one end thereof to define a leaf support ledge 43. A channel 45 is present in platform 41, and is defined, as shown in FIGS. 5A, by a cylindrical plunger support passage 47 which extends part of the way through housing 3, and then enlarges to a cylindrical bore 48. The latter flares out to an enlarged radius where it terminates at the back of housing 3, thereby defining a shoulder 50. A pair of ears 40, 42, are formed as partial arcs about channel 45. An adjoining channel 49 is formed in leaf support ledge 43 and is seen to be in communication with the forward part of passage 47. Bore 48 at the rear of housing 3 is closed by a spring plate 22, which is formed of plastic or the like and is received at shoulder 50.

Housing 3, as is seen from both FIGS. 1 and 5, is provided with a plurality of cylindrical passages 33 and with a single transversely elongated passage 53, all of which extend completely through the housing to open at the back end thereof. The passages 33 with the exception of the passage identified as 33a are used to carry diodes 35 therein. It is evident that when such diodes are nested in passages 33, the leads 35a and 35b thereof are accessible for connection at both ends of passage 33. The excepted passage, 33a, is utilized for nesting the metal contact pin 19 which via its lead 19a permits external common connection to contact plate 5. The elongated passage 53 is also seen to be adapted for receipt therein in side-by-side fashion of both a diode and a resistor. In a representative application of the present switch, up to 10 diodes and one resistor may actually be present in housing 3, with connection to an underlying circuit board being directly effected at the exposed leads of the electrical components such as at 35b. This large number of selfcontained diodes means in practice that the switch 1 can typically be i used to provide a very full range of control and encoding in the keyboard in which it is incorporated. Typically, for example, sufficient switched connections are available to provide encoding for up to seven bit numbers (including an additional bit for parity), plus additional switched connections for roll-over, shift inhibit, and control inhibit functions.

The metallic contact plate 5 is seen in FIG. 1 to be adapted to rest upon platform 41 with the two protruding bosses 55 and 57 passing through aligned holes 59 and 61 in the plate. A series of circular holes 39 and an elongate slot 63 are present in plate 5, these elements being upon assembly registrable with the various underlying passages in housing 3. In similar fashion the rectangular opening 65 registers with channel 45 in the housing. A tab 67 at the bottom of plate 5 assists in positioning the plate during assembly and closes the forward part of channel 49.

Contact leaf 7, as is seen in FIG. 1, is a metallic, leaflike structure, typically formed of a thin gauge spring steel. It is a single, unit stamped structure, including a base portion 69 which is bifurcated into the branches 23 and 25, the branches in turn being trifurcated at their adjacent but noncontacting end portions into sets of three contact fingers 23a, 23b, 23c, and 25a, 25b, 25c. Each individual contact finger is seen to be relatively independently displaceable transverse to the general plane of leaf 7. It will also be seen that each of the fingers 23a, 25a, etc., are bent downwardly at their midpoints 70 so that the ends thereof are normally displaced somewhat in the direction of plate 5.

It is seen that when the various elements are assembled in switch 1, the base portion ,69 of leaf 7 restsupon ledge 43 with the bosses 71 and 73 of the ledge protruding through circular'holes 75 and 77 in the leaf. An additional circular hole 79 in the leaf permits passage of the contact pin 21 (the head thereof being held at the leaf) through an aligned passage 81 in housing 3. It will be clear that when plate Sand leaf 7 are mounted in housing 3 the leaf 7 is only supported at its base 69, with branches 23 and 25 being cantilevered over the spaced plate 5.

Contact between the contact leaf 7 and plate 5 is effected by an operators depressing key top 11. As is best seen in FIGS. 4 and 4A, the interior of the key top 11 is formed with a pair of ribs 83 and 85 and a supporting block 87 having a cavity 89 adapted to receive end portion 91 and cross rib 92 of plunger 9 therein.

The plunger 9, which is seen both in FIG. I and in the detail drawings of FIGS. 3, 3A and 38, may conveniently be molded (of plastic or the like) as a single unit. It includes, in addition to end portion 91 and crossrib 92, a pad portion 93, and a foot portion 95. The latter, which is approximately cylindrical in shape, is adapted to pass through the openings 97 and 65 of contact leaf 7 and contact plate 5, and into channel 47 of housing 3. Portion includes a longitudinal slot 99 extending along one side thereof. Slot 99 cooperates with a key way 100 extending into housing 3 from the edge of car 42 to the back of passage 47, so as to assure that even when plunger 9 is at its-most withdrawn position, very little wobble is evidenced at key top 11. Foot portion 95 terminates in a tip 102 which is heat flattened after passage through retaining washer 106 to prevent withdrawal of plunger 9 from the housing. A return spring 17 bears against spring plate 22; spring 17, as key top 11 is depressed, is compressed, and pro- ,vides a restoring force via washer 106 for returning the key top to its original position.

By examining FIGS. 3,, 3A and 3B in conjunction with the cutaway isometric view of FIG. 2, it may be seen that plunger 9 is provided on side of foot portion 95, with a depressed flattened portion 29 adapted to receive a portion of the tactile ball 13 therein. The showing of FIG. 2 depicts the switch 1 of F IG. 1 rotated 90 in a counter-clockwise direction. Tactile ball 13 is a small plastic or metallic ball of radius larger than the height of the shoulder 104 defined (FIG. 3) between portion 29 and the unflatt-ened portion of foot 95. Ball 13 is biased into contact with face 101 by the tactile spring 15 nested in cavity 103 of housing 3,. The cutaway view of FIG. 2 depicts the switch 1 in its normal," undepressed condition. Thus it is seen that under these circumstances tactile ball 13 is firmly seated upon flat 2-9 and against shoulder 104, and in combination with the restoring force provided by spring 17, offers considerable resistance to downward movement of plunger 9, in that such, movement cannot occur until ball 13 is displaced away from the stop provided by shoulder 1 04, Upon the operators continuing to increase his fingerrpressure upon key 11, however, a threshold level is reached upon which ball 13 suddenly moves outwardly from 29 and over shoulder 104, in consequence of which a sudden precipitous drop in resistance to movement of the key occurs.

The sequence of events described, has several very important consequences in the present invention. Firstly it will be evident that a most excellent tactile feedback is present for the keyboard operator, in that the latter may mostreadily sense the sudden disengagement of tactile ball 13 and has a clear indication of key depression. Secondly, the comparatively high threshold force required to displace ball 13 eliminates the phenomenom of teasing" whereby an operator may play with-a key and accidentally activate it. Thirdly, oncesufficient force is applied to displace the ball 13, the resistance drops so suddenly that much excess force is then present, assuring a complete driving home of plunger 9 to provide a clear hit" on the switch.

Actual electrical contact in switch 1 is then brought about by pad 93 bearing against fingers 23a, 23b, 23c, and 25a, 25b, 25c. Such action is evident both from the exploded view of FIG. 1 and the cutaway view of FIG. 2. It will also be evident from these views that as the pad 93 advances, flexure occurs in both the branches 23 and 25, and in the fingers 23a, 23b, 23c, and 25a, 25b, 25c, in turn advancing these elements toward plate 5. It will also be clear that the tips of the six fingers will make initial contact with plate 5, butthat as plunger 9 advances further, flexure of branches and fingers will laterallydisplace the points of contact in a continuing wiping action.

It is important to appreciate that the six fingers 23a, 25a, etc. provide six separate contact points for the closing of the switch. Not only is thecontact resistance in such an arrangement quite low, but moreover the reliability of operation is much enhanced by the largely independent movement and contact made by the individual fingers. In addition, as has been previously pointed out, the ensuing contact between fingers and plate 5 is a wiping contact produced by a continuing impulse, in consequence of which exceedingly little bounce can occur as the switch circuit is closed.

While the present invention has been particularly described in terms of a specific embodiment thereof, it will be evident in view of the present disclosure, that t numerous variations Upon the ll'lvelltlol'l are HOW 61'1- mately in parallel spaced relationship to said plate, 7

said leaf comprising a base portion, a branch portion extending from said base portion, and multiple contact fingers connected to said branch portion and cantilevered over said contact plate;

d. plunger means adapted to bear upon said contact fingers and displace them into contact with said contact plate to close said switch;

e. a key top engageable with the top of said plunger means; and

f. means for connecting said leaf and plate to an electrical circuit for control by said switch.

2. Apparatus in accordance with claim 1 wherein said plunger means carries a depressed portion on a face thereof parallel to the direction of said displacement, and wherein said switch further includes a tactile ball and a tactile spring nested in said housing for biasing said ball against said plunger face, said spring and ball being nested at a positionsuch that when the plunger is in an undepressed position the tactile ball rests in said depressed portion and thereby provides a resistive force to displacement of said plunger, sufficient force upon said plunger acting to move said plunger and displace said ball outwardly from said depressed portion whereby to suddenly reduce the said resistive force and provide tactile indication to the operator of movement of 'said plunger.

3. Apparatus in accordance with claim 2 wherein said base and finger portions of said leaf surround and define an opening in said leaf, an opening being present in said contact plate, and a plunger support passage being present in said housing, and wherein said plunger includes a foot portion adapted to pass through said openings and into said passage of said housing and a laterally extending pad portion which presses against said fingers of vsaid contact leaf to effect said displacement thereof as said pad contacts said leaf.

4. Apparatus in accordance with claim 3 wherein said foot is of generallycylindrical shape, said depressed portion. thereon comprising a flat on said cylinder, the said tactile ball resting against the shoulder defined between said flat and the remaining portion of said cylinder when said plunger is in an undepressed condition.

5. Apparatus in accordance with claim 3 wherein said plunger support passage includes a keyway extending longitudinally therein and said plunger foot includes a longitudinal slot for engaging said keyway and steadying the lateral movement of said plunger, whereby to reduce wobble at said key top.

6. Apparatus in accordance with claim 1 wherein said housing is formed with a transverse platform for supporting said contact plate, said platform being stepped upwardly at an end thereof to define a narrow support ledge for the base portion of said contact leaf.

7. Apparatus in accordance with claim 1 wherein said housing further includes a plurality of passage ways about the periphery of said platform extending through the body of said housing to the back side thereof, said passage ways being adapted to receive diodes therein with the leads of the diodes being accessible from both sides of said passage ways, and where said contact plate further includes a plurality of openings registrable with the said passage ways in said housing, whereby to readily connect said plate to said diodes.

8. The switch of claim 1 wherein the contact fingers are substantially parallel and extend substantially at right angles to the branch portion in substantially the same plane as the branch portion.

9. The switch of claim 1 wherein the contact leaf comprises a pair of branch portions extending from said base portion and branching into multiple contact fingers.

10. The switch of claim 9 wherein the branch portions and finger portions are located in substantially the same plane.

11. The switch of claim 10 wherein the base portions, the branch portions and the fingers of said leaf surround and define an opening in said leaf.

12. A low profile keyboard switch comprising in combination:

a. a switch housing;

b. a contact plate mounted in said housing;

c. a contact leaf supported in cantilevered fashion in said housing, said leaf being positioned approximately in parallel spaced relationship to sald plate, said leaf comprising a base portion, a branch portion extending from said base portion, and multiple contact fingers connected to said branch portion and cantilevered over said contact plate, the contact fingers of said branch portion being substantially in the plane of the branch portion and extending in a direction significantly different from that of the branch portion so that at least one contact finger is considerably closer to the base portion than at least one other contact finger;

d. plunger means adapted to bear upon said leaf and I displace the cantilevered portion thereof into contact with said contact plate to close said switch; e. a key top engageable with the top of said plunger means; and f. means for connecting said leaf and plate to an electrical circuit for control by said switch. 13. The switch of claim 12 wherein the contact fingers are substantially parallel to one another and are at substantially right angles to the branch portion.

14. The switch of claim 12 wherein there are two spaced-apart branch portions extending from the base portion of the leaf and the contact fingers of the two branch portions extend toward one another. 

1. A low proFile keyboard switch comprising in combination: a. a switch housing; b. a contact plate mounted in said housing; c. a contact leaf supported in cantilevered fashion in said housing, said leaf being positioned approximately in parallel spaced relationship to said plate, said leaf comprising a base portion, a branch portion extending from said base portion, and multiple contact fingers connected to said branch portion and cantilevered over said contact plate; d. plunger means adapted to bear upon said contact fingers and displace them into contact with said contact plate to close said switch; e. a key top engageable with the top of said plunger means; and f. means for connecting said leaf and plate to an electrical circuit for control by said switch.
 2. Apparatus in accordance with claim 1 wherein said plunger means carries a depressed portion on a face thereof parallel to the direction of said displacement, and wherein said switch further includes a tactile ball and a tactile spring nested in said housing for biasing said ball against said plunger face, said spring and ball being nested at a position such that when the plunger is in an undepressed position the tactile ball rests in said depressed portion and thereby provides a resistive force to displacement of said plunger, sufficient force upon said plunger acting to move said plunger and displace said ball outwardly from said depressed portion whereby to suddenly reduce the said resistive force and provide tactile indication to the operator of movement of said plunger.
 3. Apparatus in accordance with claim 2 wherein said base and finger portions of said leaf surround and define an opening in said leaf, an opening being present in said contact plate, and a plunger support passage being present in said housing, and wherein said plunger includes a foot portion adapted to pass through said openings and into said passage of said housing and a laterally extending pad portion which presses against said fingers of said contact leaf to effect said displacement thereof as said pad contacts said leaf.
 4. Apparatus in accordance with claim 3 wherein said foot is of generally cylindrical shape, said depressed portion thereon comprising a flat on said cylinder, the said tactile ball resting against the shoulder defined between said flat and the remaining portion of said cylinder when said plunger is in an undepressed condition.
 5. Apparatus in accordance with claim 3 wherein said plunger support passage includes a keyway extending longitudinally therein and said plunger foot includes a longitudinal slot for engaging said keyway and steadying the lateral movement of said plunger, whereby to reduce wobble at said key top.
 6. Apparatus in accordance with claim 1 wherein said housing is formed with a transverse platform for supporting said contact plate, said platform being stepped upwardly at an end thereof to define a narrow support ledge for the base portion of said contact leaf.
 7. Apparatus in accordance with claim 1 wherein said housing further includes a plurality of passage ways about the periphery of said platform extending through the body of said housing to the back side thereof, said passage ways being adapted to receive diodes therein with the leads of the diodes being accessible from both sides of said passage ways, and where said contact plate further includes a plurality of openings registrable with the said passage ways in said housing, whereby to readily connect said plate to said diodes.
 8. The switch of claim 1 wherein the contact fingers are substantially parallel and extend substantially at right angles to the branch portion in substantially the same plane as the branch portion.
 9. The switch of claim 1 wherein the contact leaf comprises a pair of branch portions extending from said base portion and branching into multiple contact fingers.
 10. The switch of claim 9 wherein the branch portions and finger portions are located in substantially the same plane.
 11. The switch of claim 10 wherein the base portions, the branch portions and the fingers of said leaf surround and define an opening in said leaf.
 12. A low profile keyboard switch comprising in combination: a. a switch housing; b. a contact plate mounted in said housing; c. a contact leaf supported in cantilevered fashion in said housing, said leaf being positioned approximately in parallel spaced relationship to saId plate, said leaf comprising a base portion, a branch portion extending from said base portion, and multiple contact fingers connected to said branch portion and cantilevered over said contact plate, the contact fingers of said branch portion being substantially in the plane of the branch portion and extending in a direction significantly different from that of the branch portion so that at least one contact finger is considerably closer to the base portion than at least one other contact finger; d. plunger means adapted to bear upon said leaf and displace the cantilevered portion thereof into contact with said contact plate to close said switch; e. a key top engageable with the top of said plunger means; and f. means for connecting said leaf and plate to an electrical circuit for control by said switch.
 13. The switch of claim 12 wherein the contact fingers are substantially parallel to one another and are at substantially right angles to the branch portion.
 14. The switch of claim 12 wherein there are two spaced-apart branch portions extending from the base portion of the leaf and the contact fingers of the two branch portions extend toward one another. 